Titanium for CNC Machining: Grades, Tooling, Heat, Tolerances and Applications

1. What Titanium Buys You on a CNC Part

You buy titanium for one of four working properties: strength-to-weight, corrosion resistance, non-magnetic behavior, or biocompatibility. Each one maps to a family of parts.

Density and specific strength. Grade 5 (Ti-6Al-4V) sits at 4.43 g/cm³, versus 7.85 g/cm³ for 1018 steel and 2.70 g/cm³ for 6061 aluminum (ASM Handbook Vol 2). B348 Table 2 sets the Grade 5 UTS floor at 895 MPa, so specific strength lands above most CNC-grade steels. Aerospace brackets, landing-gear links and drone gimbals take titanium for the mass swing on every landing cycle.

Does titanium rust? No. The surface forms a passive TiO₂ film within milliseconds of air exposure, and the film keeps growing in salt spray, seawater, chlorinated water and diluted nitric acid. That property drives Grade 2 heat-exchanger tube sheets and Grade 7 (Ti-Pd) chemical piping.

Is titanium magnetic? No. Titanium is paramagnetic, several thousand times weaker than 304 or 316 stainless. That behavior clears Grade 23 orthopedic implants for MRI and lets titanium fasteners sit inside sensitive electronics enclosures without distorting the field.

Biocompatibility. The same TiO₂ film keeps Grade 23 (Ti-6Al-4V ELI, UNS R56407) osseointegrated in spinal cages and dental abutments. Implant service is governed by ASTM F136, not B348; the two do not substitute, and Section 10 shows why.

If your part needs any of the four, our CNC machining capability for titanium and the materials and properties reference for titanium comparisons cover the next-layer decisions.

2. Titanium Grades That Show Up in CNC RFQs

The word titanium on a drawing covers at least nine alloys in common CNC RFQs. The table below pulls the UNS numbers and alloying intent straight from ASTM B348/B348M-25 Table 1.

Grade	UNS	ASTM B348 Identification	Where It Shows Up
1	R50250	Unalloyed Ti, lowest oxygen ceiling	Cryogenic vessels, gasket seats
2	R50400	Unalloyed Ti, standard oxygen	Heat exchanger tube sheets, marine plate
2H	R50400	Same chemistry as Grade 2, higher UTS floor (400 MPa)	Pressure vessels per B348 Note 1
3	R50550	Unalloyed Ti, medium oxygen	Airframe skins, engine housings
4	R50700	Unalloyed Ti, highest oxygen of CP series	Structural bar, high-strength fasteners
5	R56400	Ti-6Al-4V, α+β alloy	Avionics brackets, landing gear, orthopedic hardware
7	R52400	Unalloyed Ti + 0.15% Pd	Chemical piping, chlorine service
9	R56320	Ti-3Al-2.5V	Aerospace tubing, bicycle frames
12	R53400	Ti-0.3Mo-0.8Ni	Marine desalination, chemical vessels
23	R56407	Ti-6Al-4V ELI, low interstitial	Spinal implants, dental abutments

Two mix-ups burn RFQs the most. First, Grade 5 and Grade 23 are not interchangeable: Grade 5 caps oxygen at 0.20 wt% and Grade 23 caps it at 0.13 wt% per B348 Table 1, and only Grade 23 satisfies the low-interstitial ceiling ASTM F136 requires for implants. Second, the H suffix (Grade 2H, 7H, 16H, 26H) does not change chemistry; it only guarantees a higher minimum UTS of 400 MPa for pressure-vessel service (B348 Note 1). Writing Grade 2H when you meant a stronger alloy is a mis-spec; you meant Grade 5 or 23.

The oxygen ladder in the CP series (0.18, 0.25, 0.35, 0.40 wt% ceilings across Grades 1 to 4) sets minimum strength floors, not machining difficulty.

3. ASTM B348 in Practice: Chemistry, Mechanicals, and Delivery Condition

B348 defines three things that show up on your MTR: chemistry ceilings, minimum room-temperature tensile properties, and delivery condition.

Chemistry. Oxygen weight-percent caps set the strength floor. B348 Table 1: Grade 1 at 0.18, Grade 2 at 0.25, Grade 3 at 0.35, Grade 4 at 0.40, Grade 5 at 0.20, Grade 23 at 0.13. Hydrogen caps at 0.015 wt% for most grades and drops to 0.0125 wt% for Grade 23 to protect ductility for implant service. The mill samples ingot top and bottom for chemistry plus a hydrogen sample on the delivered form (B348 §9.1 to §9.3).

Mechanicals. Table 2 minima below apply to longitudinal specimens with section thickness ≤ 3 in [76 mm] and cross-section ≤ 10 in² [64.5 cm²] (Note A). Sections above those limits need supplier-agreed values.

Grade	UTS min MPa [ksi]	0.2% YS min MPa [ksi]	Elong. min %	RA min %
1	240 [35]	138 [20]	24	30
2	345 [50]	275 [40]	20	30
2H	400 [58]	275 [40]	20	30
3	450 [65]	380 [55]	18	30
4	550 [80]	483 [70]	15	25
5	895 [130]	828 [120]	10	25
9	620 [90]	483 [70]	15	25
12	483 [70]	345 [50]	18	25
23	828 [120]	759 [110]	10	25

These are minimum acceptance values from tensile testing per ASTM E8/E8M, not design allowables. Design allowables come from MMPDS or MIL-HDBK-5J using A-basis or B-basis statistics; substituting a B348 minimum into a fatigue calculation is a common RFQ mistake.

Delivery condition. B348 scope is annealed material. For Grade 9, 18, 20, 21, 23, 28 and 29, §4.1.4 requires the order to state the condition. Transformed-beta and solution-treated-and-aged (STA) conditions appear in Table 2 with different tensile floors and lower elongation. “Titanium bar” on a PO is not enough for those grades; write “Grade 23 annealed” or “Grade 23 STA moderate strength” per §4.1.4.

4. Raw Stock: Bar, Billet, Rod, Sheet, Plate for CNC

Once grade and condition are locked, the next line on the RFQ is product form. B348 covers bar and billet only. Sheet, plate, tube and forgings sit under separate ASTM specifications (B265 for sheet and plate, B338 for tube, B381 for forgings).

Bar vs billet. §3.1.1 defines bar as hot-rolled, forged, extruded or cold-worked solid material with cross-section ≤ 16 in² [10,323 mm²]. Billet (§3.1.2) is hot-worked from an ingot above those limits, with width under five times thickness. Extruded bar is approved on the standard only for the unalloyed grades (Grade 1 to 4); extrusion of Grade 5, 9, 12 or 23 requires supplier agreement.

Size tolerances. B348 assigns eight tables (Tables 4 to 11) by shape, working method and dimension band. There is no single “B348 diameter tolerance.” Table 7 gives cold-worked round bar in the >0.5 to <1 in [12.70 to <25.40 mm] band a diameter tolerance of ±0.002 in [0.05 mm]; the Table 7 footnote doubles that if the bar is heat-treated or pickled after cold work.

Surface as delivered. §8.1 lets the mill deliver annealed material descaled, sandblasted, ground or rough-turned. Ra targets come from your drawing and fall under Section 8, not from the mill delivery state.

On our aerospace case TI-5-2408-AHB-017 (Ti-6Al-4V avionics bracket, 48 pcs), we ordered Grade 5 plate at 152.4 × 101.6 × 25.4 mm (EPOC CRAFTER shop-floor data). The MTR reported UTS 963 MPa and 0.2% YS 894 MPa on the delivered plate, above the 895 and 828 MPa floors B348 Table 2 sets for Grade 5. Cutting plate close to final envelope beat oversize round bar on this job: less swarf, shorter cycle time, lower chip-trap risk on a bracket with 20 mm deep pockets. Our CNC machining quote checklist for titanium bar and billet covers what to send with the first RFQ.

5. Why Titanium Is Hard to Machine (Heat, Galling, Work Hardening)

Three properties fight you when the tool touches Grade 5 or Grade 23.

Heat concentrates at the cutting edge. Titanium thermal conductivity is about 6.7 W/m·K per ASM Handbook Vol 2, roughly one-sixth of 6061 aluminum (167 W/m·K) and one-third of 316 stainless (16 W/m·K). Heat has nowhere to go, so it stays in the tool. Push Sfm up 20% and tool life drops disproportionately.

Galling and built-up edge. Titanium reacts with W, Fe and Co above 500 °C. Chips weld to the flute if the coating fails or coolant drops away. The signature failure is a shiny welded ring at the edge followed by chipping on the next pass. Uncoated carbide fails inside minutes on Grade 5.

Deflection and work hardening. Ti-6Al-4V Young’s modulus is about 114 GPa, against 200 GPa for steel. A slender end mill flexes further under the same radial cut, so you drop radial engagement or feel it as chatter. Idle rubbing without cutting hardens the surface, so lingering at zero chip load is where work-hardened rework starts.

6. Tooling, Speeds, Feeds, and Coolant for Common Grades

Coating. AlTiN and TiAlN survive above 800 °C at the flank and stay non-reactive with Ti-6Al-4V. Skip plain TiN; the film breaks down and titanium chips weld to the exposed carbide.

Speeds and feeds by grade (published starting bands).

Grade	Surface speed (m/min)	Feed per tooth (mm)	Notes
Grade 2 (CP)	60 to 120	0.05 to 0.15	Softer, allow higher IPT
Grade 5 (Ti-6Al-4V)	40 to 90	0.03 to 0.10	Reduce as pocket depth grows
Grade 23 (ELI)	35 to 80	0.03 to 0.08	Low O gives lower shear strength; ELI still hardens

Sources: Sandvik Coromant Machining Guide (Ti-6Al-4V section) and Kennametal Application Guide for Titanium. Starting bands, not spec.

Coolant. Flood coolant at low pressure leaves chips in the cut zone. High-pressure coolant (HPC) at 40 to 70 bar through the spindle evacuates chips and forces flash boiling on the flank. Cryogenic LN₂ cuts flank temperature further but adds capital and consumable cost; on 48 to 200 piece batches, HPC still gives better tool-life economics.

Case: TI-5-2408-AHB-017. For the aerospace Ti-6Al-4V avionics bracket (48 pcs, 20 mm deep pockets), the shop ran a Sandvik CoroMill Plura 1P342-1200-XA 1730 AlTiN 12 mm on a Haas VF-4SS with 69 bar through-spindle HPC. Three-stage parameters:

Stage	Surface speed (m/min)	IPT (mm)	ap (mm)	ae (mm)	ae as % of D
Roughing	55	0.045	8.0	1.2	10%
Semi-finishing	70	0.035	3.0	0.6	5%
Finishing	85	0.025	1.0	0.2	1.7%

Cycle landed at 54.8 min per bracket and tool life at 18 pieces per tool (EPOC CRAFTER shop-floor data). Dewey Wu: “For Grade 5 titanium pockets deeper than 20 mm, we keep radial engagement near 10% D and use 69 bar through-spindle coolant because chip evacuation, not spindle power, becomes the limiting factor.”

For turned features on Grade 5 shafts and bearing seats, step turning on CNC lathes handles titanium shaft shoulders with the same coolant discipline.

7. Titanium Machining Tolerances, Thin Walls, and Distortion

Tolerance on titanium moves with wall thickness, tool overhang, setup rigidity and inspection method.

Achievable envelopes on Grade 5. With a rigid setup, sharp AlTiN-coated carbide and HPC, EPOC CRAFTER holds:

Feature	Achievable envelope	Condition
Linear dimension	±0.025 mm (IT7) on features under 100 mm	Rigid workholding, tool stickout ≤ 3× D
Reamed hole	H7 (Ø6.000 +0.012/0)	Chatter-free reamer entry, HPC at bore
Profile	±0.020 mm on part outline	Fully constrained fixture
Flat, parallel	0.02 mm per 100 mm	Post-roughing stress relief for plates >20 mm
Ra machined	0.8 to 1.6 μm	Finish pass at 0.2 mm ae, 85 m/min
Ra polished or blasted	0.4 to 0.8 μm	Covered in Section 8

Working envelopes, not guarantees. Wall thickness under 1.5 mm on Grade 5 costs roughly one IT grade per 0.3 mm reduction (EPOC CRAFTER engineering note). Below 1.0 mm, plan two-setup toolpaths and stress relief between passes.

Distortion. Plate stress plus asymmetric material removal warps the part after clamp release. On plates thicker than 20 mm, we rough balanced pocket depth on both sides before finishing, and we save datum-critical faces for the last setup after stress redistributes.

Case: TI-5-2408-AHB-017. The drawing called profile ±0.05 mm, hole position Ø0.05 mm to A|B|C, and Ø6.000 +0.010/0 mm on the reamed locating holes. Final CMM inspection on a ZEISS CONTURA G2 reported profile within ±0.018 mm, hole position 0.028 mm max, and reamed diameters between Ø6.004 and Ø6.008 mm. Ra came in at 0.74 μm on the locating pads and 1.18 μm on the pocket floor, both inside the 0.8 and 1.6 μm callouts. 46 of 48 first-article parts passed dimensional check on the first cut; two required burr rework; batch yield closed at 100% (EPOC CRAFTER shop-floor data). Dewey Wu: “The datum pads were finished after stress-balanced roughing, so the Ø6.000 mm locating holes stayed within Ø6.004 to Ø6.008 mm after final inspection instead of drifting with clamp release.”

Rigid setup planning on Grade 5 thin walls draws on our DFM design guidelines for thin-wall parts, and the tolerances and standards reference gives the wall-to-tolerance mapping we use in RFQ review.

8. Surface Finish, Anodizing and Passivation for Titanium

Titanium post-machining takes three finish routes across aerospace, medical and consumer BOMs.

Anodizing (Type II decorative vs Type III hardcoat). Titanium anodizing does not deposit a coating; it grows the TiO₂ film thicker and controls interference color by voltage. Type II runs 10 to 100 V in a neutral electrolyte and produces bronze, purple, blue and green colors used on surgical instruments for size coding and on consumer parts for identification. Type III runs higher voltage in a different electrolyte and grows a thicker, wear-resistant oxide used on aerospace linkages. Type III on titanium is chosen for wear, not for corrosion.

Passivation per ASTM F86 for medical titanium. Passivation removes free iron picked up from carbide and fixturing during machining and reinforces the TiO₂ film. ASTM F86 is the reference standard for medical titanium; ASTM A967 is written for stainless steel. Common bath: 20 to 40 vol% HNO₃ at ambient temperature, 20 to 30 minutes.

Bead blasting and polishing. Fine glass bead blasting gives a uniform matte finish at Ra 0.8 to 1.6 μm and closes machining tool marks. Mechanical polishing on Grade 5 reaches Ra 0.2 μm on flats but work-hardens the surface, so complex geometries move to abrasive tumbling.

Case: TI-5-2408-AHB-017. After CNC, the 48 avionics brackets went through fine glass bead blasting followed by nitric acid passivation at 25 vol% HNO₃ for 30 minutes per ASTM F86 methodology (EPOC CRAFTER shop-floor data). MTR, blast log and passivation record shipped with the parts.

The color specification and the anodize, passivate and blast workflow on titanium tie back to our surface finishing options for anodizing and passivation.

9. Welding and Heat Treatment When Titanium Parts Are Fabricated

TIG (GTAW) is the standard. Titanium above 500 °C reacts with atmospheric oxygen and nitrogen fast enough that a normal open-arc TIG puddle contaminates on contact. Shielding runs three layers: primary argon at 15 to 20 L/min through the torch, trailing argon covering the cooling bead, and backing gas on the root side (or a full argon-purge chamber for thin sheet). AWS A5.16 covers filler wire selection; common matches are ERTi-2 for Grade 2, ERTi-5 for Grade 5 and ERTi-23 for Grade 23 implants.

Read the color. Weld color per AWS D17.1 practice is the fastest shielding-quality check: silver or light straw is acceptable, dark straw is marginal, blue is borderline, grey or white powder is reject. Grinding out a blue tint and re-welding does not fix the root cause; check gas coverage first.

Interpass temperature. Hold interpass below about 150 °C on Grade 5 to keep grain growth and alpha case low.

Heat treatment. Stress relief on Grade 5 runs 595 to 650 °C for 1 to 4 hours per AMS 2801 practice; full anneal runs about 730 °C for 2 hours air-cooled. Grade 23 in STA moderate strength condition (B348 Table 2) solution-treats at 900 to 950 °C, water-quenches, then ages 480 to 540 °C for 4 to 8 hours. These are practice bands; the actual cycle traces to the customer PO or the applicable AMS.

Weld parameters and post-weld machining connect back to the broader mechanics laid out in our welding process families and HAZ control article.

10. MTR, Certificates, and the B348/F136/AMS 4928 Boundary

An MTR (Material Test Report, also called mill test certificate or MTC) turns a titanium bar into a certified aerospace or medical part. B348 §15.1 requires the mill to certify the delivered material meets the standard and to record chemistry, tensile results, condition, and manufacturing method (hot rolled, forged, extruded or cold worked). §16 requires heat-number marking on the bar plus part-level identification on packaging.

B348 is not F136 and not AMS 4928. Grade 5 bar to B348 with UNS R56400 does not automatically satisfy ASTM F136 for surgical implant service, which imposes tighter interstitials and calls out Grade 23 (Ti-6Al-4V ELI, UNS R56407). Grade 5 bar to B348 does not automatically satisfy SAE AMS 4928 either, which covers aerospace bar and forging stock with acceptance criteria on ultrasonic inspection, macro-etch and micro cleanliness on top of B348 chemistry and mechanicals. Cross-writing the three on an RFQ (for example, “B348 Grade 5 implants”) stalls the order at MTR review.

Case: TI-5-2408-AHB-017. The paperwork package that shipped with the 48 avionics brackets was the MTR to B348/B348M-25, the FAI report per AS9100D workflow, and the passivation record per ASTM F86 (EPOC CRAFTER shop-floor data). Dewey Wu: “For aerospace titanium RFQs, we treat the MTR, heat number, passivation record and FAI report as part of the part, because missing paperwork can block assembly release even when dimensions pass.”

The paperwork discipline is documented in our quality and certification workflow behind every MTR, and the vetting we run on a new mill is broken down in how to evaluate a CNC supplier before signing off an MTR.

11. Titanium Cost and When It Is Worth Machining vs Substituting

Titanium cost hits the invoice through four levers: raw stock price, cycle time, tool consumption and certificate work.

Raw stock. Grade 5 mill plate and bar run several times the $/kg of 6061 aluminum because the Kroll process and vacuum arc remelt consume energy and chlorine chemistry. Published aggregators put Grade 5 bar at roughly 5 to 10 times 6061-T6 bar on a $/kg basis, moving with heat-treat lot, certificate level (industrial B348 vs aerospace AMS 4928) and market swings. Get a live quote before you cost a program.

Cycle time. Grade 5 mills at surface speeds two to three times slower than 6061-T6 with lower feed per tooth, so the same pocket takes several times longer at the machine. Our TI-5-2408-AHB-017 avionics bracket ran 54.8 min per part in Ti-6Al-4V; the same geometry in 6061-T6 would land near 12 to 15 min on the same Haas VF-4SS (EPOC CRAFTER engineering note).

Tool consumption. Grade 5 wears AlTiN-coated carbide roughly 4 to 6 times faster than 6061-T6 in comparable pocketing. On the bracket run, one 12 mm CoroMill Plura processed 18 brackets before replacement (EPOC CRAFTER shop-floor data).

Certificate work. MTR handling, FAI to AS9100D and passivation records per ASTM F86 add hours to the quality department, not the shop.

When to substitute. If the part does not need one of the four titanium value properties from Section 1, price out 17-4 PH stainless (for strength) or 7075-T6 aluminum (for weight, non-magnetic behavior) before committing to Ti. Sizing a substitution runs through our CNC part weight calculator to estimate titanium blank cost against equivalent aluminum or steel weight.

12. Titanium vs Steel, Stainless, Aluminum, Inconel, Tungsten

Grade 5 wins on density, corrosion, thermal service and cost against most alternates. The comparison below uses published values, not design allowables.

Property	Ti-6Al-4V Grade 5	4140 alloy steel	316L stainless	6061-T6 aluminum	Inconel 625	Pure tungsten
Density (g/cm³)	4.43	7.85	8.00	2.70	8.44	19.30
UTS (MPa)	950	950	515	310	900	550
Yield (MPa)	880	655	205	275	490	550
Thermal cond. (W/m·K)	6.7	42	15	167	10	173
Machinability index (steel = 100)	~22	65	45	360	~15	~5
Cost band (rel. to 316L bar)	4× to 8×	0.6×	1×	0.5× to 0.8×	3× to 6×	8× to 15×

Sources: ASM Handbook Vol 2 for physical and mechanical properties; Sandvik Coromant and Kennametal application guides for approximate machinability index; distributor pricing surveys for cost bands.

Choose Grade 5 over 316L when strength-to-weight matters and marine or biofluid corrosion has to be answered. Grade 5 is roughly half the density of 316L at nearly twice the UTS, and it does not stress-corrosion-crack in warm chloride the way 316L can.

Choose Grade 5 over 7075-T6 when service temperature exceeds 150 °C (7075 loses strength quickly) or non-magnetic behavior matters near sensitive electronics.

Choose Inconel 625 over Grade 5 above 400 °C service (Grade 5 loses strength; Inconel holds to 815 °C) and where hot corrosion by sulfidation is on the failure sheet.

Choose tungsten only for radiation shielding, density-critical counterweights or extreme high-temperature electrodes; you pay for it in tool life and cost.

13. Applications: Aerospace, Medical, Marine, Consumer

Aerospace: Grade 5, Grade 9, Grade 23. Airframe fasteners, engine mounts, bleed-air ducting, avionics brackets, landing-gear links. Grade 5 covers most structural work under AMS 4928 (bar and forging) and AMS 4911 (sheet). Grade 9 Ti-3Al-2.5V goes into hydraulic and pneumatic tubing under AMS 4943 for weldability and lower cost per foot.

Medical: Grade 23 (Ti-6Al-4V ELI), Grade 4 CP. Spinal cages, femoral stems, pedicle screws, dental abutments, orthopedic plates. Implant service requires ASTM F136 for Grade 23 or ASTM F67 for CP grades; B348 material alone does not certify for implants. Our medical devices manufacturing line for Grade 23 parts runs the certification workflow that connects B348 raw stock to F136-compliant implant billet.

Marine and chemical: Grade 2, Grade 7, Grade 12. Seawater heat-exchanger tube sheets, desalination pumps, pulp and paper bleach lines, chlorine service piping. Grade 7 adds 0.15 wt% palladium for extreme acid service; Grade 12 (Ti-0.3Mo-0.8Ni) handles brine crevice corrosion better than Grade 2.

Consumer and sports: Grade 5, Grade 9. Bicycle frames, high-end watch cases, camping utensils, folding knives. Grade 9 dominates road-bike tubing for weldability and specific stiffness; Grade 5 shows up in premium watch cases where scratch resistance and non-magnetic behavior both matter.

14. FAQ

Is titanium magnetic?

No. Titanium is paramagnetic, thousands of times weaker in magnetic response than 304 or 316 stainless. Grade 23 orthopedic implants clear MRI screening on that behavior, and titanium fasteners work inside sensor housings without distorting the field.

Does titanium rust?

No. Titanium forms a passive TiO₂ film within milliseconds of air exposure, and the film keeps growing in seawater, chlorinated water and diluted nitric acid. Rust in the ferrous sense does not form. Aggressive HF and reducing conditions still attack it; palladium-alloyed Grade 7 handles those.

Why is titanium so expensive?

Two reasons stack. Kroll process feedstock (Mg reduction of TiCl₄) is energy-intensive, and every mill lot is vacuum arc remelted for chemistry control. Bar and billet then carry the certificate cost of B348 or AMS testing. Downstream, low thermal conductivity forces slow cutting, so the machined-part invoice compounds.

Is titanium harder to machine than stainless steel?

Yes. Grade 5 machinability index sits near 22 against a 100 steel baseline; 316L sits near 45. Grade 5 needs AlTiN-coated carbide, HPC at 40 to 70 bar, feed per tooth of 0.03 to 0.10 mm, and radial engagement dropped as pocket depth grows.

What is the difference between Grade 5 and Grade 23 titanium?

Grade 5 (Ti-6Al-4V, UNS R56400) caps oxygen at 0.20 wt% and covers industrial and aerospace parts. Grade 23 (Ti-6Al-4V ELI, UNS R56407) caps oxygen at 0.13 wt% and hydrogen at 0.0125 wt%, and only Grade 23 satisfies ASTM F136 for surgical implants. Do not substitute in either direction.